How long do you give an idea before you drop it?

I have a few ideas that I'm going to try to generate some adult affiliate income, but I'm really not sure how long I should let them sit while they build traffic to see if they're going to work. I think I usually give up too soon like I'll schedule a bunch of posts and/or tweets for a few weeks and then give up and go back to what is working for me. I do fairly well at phone sex work and phone sex affiliate programs, but I'd like to branch out and stick to it this time. How long do you usually wait?

Thanks